According to the recent gynecophysiological research and the results of practical application thereof, the basal body temperature (hereinafter referred to as BBT) method has been verified to be by far one of the most effective ways of birth control, and it is also the only allowable way of contraception for Catholics. The term BBT method, as its name implies, refers to the method involving ascertaining the date of ovulation by virtue of a series of observation of the biphasic change of body temperature. FIG. 1 shows a one-month period of a menstral cycle to find the proper period of intercourse, so as to avoid, or in the opposite sense, if any, to cause pregnancy depending on the users' preference, in other words, to become pregnant under control.
Nevertheless, it was still found difficult to put such an ideal method into extensive practice by known means in an easy, convenient way since in order to obtain a reliable curve describing the cyclic change of body temperature, frequent measurements are required to record the continuously changing body temperature to get enough "samples" to sketch a graph with the requisite reliability, therefore taking much time. Moreover, it suffers such disadvantages as the inaccuracy of the data obtained, the trouble in recording, and the tendency of forgetting the daily measurement. Besides, graphical method fails to provide useful information of the pre-ovulation safe period, i.e., it is only cabable of ascertaining the ovulation date thereafter, but unable to predict it beforehand.
Accordingly, it is the main object of the present invention to obviate and mitigate the existing defects of birth control using the BBT method, which, although appears to be effective, has seldom been practically accepted due to the foregoing technical problems thereof.